Technical White Paper
SELF-LEVELING UNDERLAYMENTS
Subsurface Tolerances and
Floor Flatness Requirements —
A Case for Cementitious
Self-Leveling Underlayments
It is common knowledge that putting more effort into surface
preparation will yield benefits in your floor covering
installation. Not only will the floor covering be easier to
install, but a truly flat floor will have an aesthetic quality that
building occupants will appreciate. While there are many
minimal industry standards for achieving a flat floor, the
question remains: Do they go far enough? As the flooring
industry continues to evolve — and architects and designers
become more demanding — construction methods must
continue to evolve as well.
By John D. Gallup, CTC, CSI
Architectural Consultatnt
Custom Building Products
Today, there is a growing demand for larger format ceramic
and natural stone tiles. This necessitates proper specification
and execution of floor surface preparation, particularly in
relation to floor flatness, which is critical to any successful
floor covering installation. To insure a higher quality
appearance and reduced life cycle cost, the ceramic tile
industry has responded to large format tile trends with
updated reference standards and guidelines that provide
more specific definitions for large format tile, as well as
tighter tolerances for substrate flatness.
Technical White Paper
SELF-LEVELING UNDERLAYMENTS
At Custom Building Products, we believe substrate flatness is best achieved through the
application of a flowable and cementitious self-leveling underlayment (SLU) and we
have developed this paper to address:
•Potential conditions in the floor subsurface and the industry’s requirements
related to them
•Proper specification and installation of a self-leveling underlayment over some
common flooring conditions and substrate types
•The benefits of specifying self-leveling underlayment and cement-based patching
and leveling compounds for all hard surface and resilient flooring products
•The performance and cost efficiencies inherent in using self-leveling
underlayment materials
Enhanced Definitions for Large Format Tile and Subsurface
Flatness Requirements
The American National Standards Institute (ANSI) Specification for the Installation of
Ceramic Tile stipulates that deviations in sub-floor flatness should be no greater than
1/4" in 10' (Ref. ANSI A108.02 – 4.0 / 4.1.4.3.1). Before the year 2010, the Tile
Council of North America (TCNA) described large format tile units as “…generally
considered to be 8" x 8" and greater”, with no provision for enhanced subsurface
tolerances when tiles 8" x 8" or larger had been selected. However, as of 2011,
subsurface tolerances for tile installation, based on tile unit size, have been updated in
the TCNA Handbook. For tiles with all edges less than 15", the maximum allowable
variation is 1/4" in 10' and no more than 1/16" in 12". For large format tiles with one
edge greater than 15" and for natural stone tiles, the maximum allowable substrate
variation can be no more the 1/8" in 10' and 1/16" in 24". When thin bed epoxy
mortars are used, the variation can be no more than 1/16" in 36" with no abrupt
irregularities greater than 1/32" (2011 TCNA Handbook). In some instances, the
architect/designer will require the more stringent finish tolerance, and the subsurface
specification or tile specification should reflect this.
In response to the new subsurface flatness criteria, a number of tile manufacturers
specializing in large format tile materials have embraced these updated floor flatness
requirements, and now include references to the new guidelines in their product technical
data sheets and installation guidelines. It is the responsibility of the architect or design
professional to include these enhanced floor flatness requirements in the project
specification. It is equally important for the architect or specifications writer to consult with
the design/interiors team (and vice versa) to insure that the specific installation requirements
and guidelines for the selected tile for the project are reflected in the tiling specification.
To achieve the required flatness tolerances, the industry is increasingly relying on selfleveling underlayments. By virtue of the SLU’s working characteristics and performance,
a flowable, cementitious self-leveling underlayment will provide flatness tolerances well
within 1/8" in 10' maximum plane variation. This provides a finished substrate that can
accept most ceramic and natural stone tile, including tile that maintains any edge of 15"
or greater, as well as all types of resilient flooring.
Traditional Straightedge Specification vs. F-Numbers
for Rating Floor Flatness
The American Concrete Institute (ACI) has adopted the so-called “f-number” system, under
the ACI 117 specification, as a way of determining the flatness (and levelness as per F/L
numbers) of concrete slabs. F-numbers are determined through testing procedures in
ASTM E-1155. These testing procedures are also referenced in ASTM F-710 for The
Preparation of Concrete Floors to Receive Resilient Flooring. Determining the flatness of a
concrete slab using the ASTM E-1155 method provides more accurate and reliable results
compared to the conventional “straightedge specification” for 1/4" in 10', and 1/8" in 10'
plane variation. Under ASTM E-1155, ACI sets forth guidelines that require specified floor
flatness be assessed within 72 hours after concrete installation, to insure accuracy.
Photo Courtesy ABW Construction – Woodinville, WA
Technical White Paper
SELF-LEVELING UNDERLAYMENTS
Where a typical straightedge method for plane variation indicates only where gaps occur
between a 10' straightedge and finished floor, floor flatness testing procedures under
ASTM E-1155 provide a more quantitative method for determining the flatness and
levelness of the entire concrete substrate. While a number of various techniques exist for
measuring concrete to determine f-numbers, perhaps the most common is the “dipstick
floor profiler” method, in which assessments are taken at a frequency of 1 ft., in both
north/south and east/west directions. Measurement lines must maintain a minimum of
11 ft., and a minimum of 34 readings per 1000 sq. ft. of floor is required. The
“dipstick” testing apparatus is broadcast along a line, which measures the variation in
surface elevation at 1 ft. intervals. A reading is recorded at a point when the dipstick is
pivoted, and the alternate “foot” of the apparatus is placed on the slab.
Photo Courtesy ABW Construction – Woodinville, WA
Project Specifications Shall Indicate the Corrective Measures
for Concrete Slabs that are not in Compliance with Project
and Condition Requirements.
Appropriate floor flatness requirements for the slab, based on conditions, intended
usage, and service requirements, can be found in ACI 302 section - Guide for Concrete
Floor and Slab Construction. Although there is no exact method of comparing f-numbers
to conventional straightedge testing results, the following chart can be used as a
guideline to approximate values between the two:
F-Number Result (FF)
Straightedge Specification Result
(Plane Variation in 10')
25
1/4"
50
1/8"
100
1/16"
F-Number Results of Self-Leveling Applications
Installing a self-leveling underlayment makes it easy to exceed the requirements of the
floor covering. Using the testing procedures outlined in ASTM E-1155, floor surfaces
covered with a cementitious SLU have rendered f-numbers in the mid to upper 80’s. The
following is one example of field test results for a floor covered with CUSTOM’s high
performance SLU:
Minimum Required Flatness/Levelness
30 Day Result using SLU
35 / 25
86.6 / 46.2
Lippage, Facial Variation of Tile Units and Craftsmanship
Lippage is an unsightly and potentially hazardous defect in a ceramic and natural stone tile
installation. It is a condition in which one edge of a tile is higher than the adjacent tile,
which gives the finished surface an uneven appearance. When tile is selected as a flooring
finish, accessibility is a key consideration, and design professionals should understand that
any plane variation in the subsurface would be reflected in the finished installation. In short,
a true and flat subsurface, within the flatness tolerances set forth in ANSI sections A108.01
and A108.02, will only minimize lippage conditions and any potential subsequent liability
issues caused by unexpected changes in the plane of the finished floor.
Facial variation of the tile units that are being considered for the installation will also
present some challenges. A tile installation with tile units maintaining any facial variation
will be made even more challenging over a subsurface that maintains a change of plane
outside of the ANSI and TCNA flatness guidelines. ANSI A108.02 – Section 4.3.8
stipulates that the grout joint width shall be at least three times the actual facial variation
of the tile. Proper surface preparation with regard to subsurface flatness tolerances will
allow for a much more efficient and less challenging tile installation, particularly when
you are dealing with non-rectified tile units which maintain a facial variation, as described
in ANSI A108.02 4.3.8. It is important to note that thin-set bond coats are intended solely
to bond the tile to the substrate. They are not formulated for use as leveling agents.
Technical White Paper
SELF-LEVELING UNDERLAYMENTS
Wood and Resilient Flooring Also Need Flat Underlayments
Just like ceramic tile, wood and resilient flooring require a high degree of flatness that
can easily be achieved using a cementitious SLU. Many manufacturers of wood flooring
require that the variation in floor flatness be no more than 3/16" in 10' and 1/8" in 6'.
The installation of wood flooring also requires that the floor be dry. Because of the rapid
curing of cementitious SLU, it is possible to achieve a dry floor that meets the industry
requirements in less than 24 hours. Many of the adhesives used to bond wood and
resilient flooring are sensitive to moisture and extreme pH readings, CUSTOM’s SLU is
formulated to balance the finished pH to accommodate most common adhesives.
Condition Requirements Prior to Application of
Self-Leveling Underlayment
It is typically recommended that SLU be applied in conditions where ambient
temperature is above 50° F, and not more than 90° F. To ensure the integrity of the
primer, the moisture vapor transmissions rate (MVTR) from the substrate should not be
in excess of 5 lbs. of water/day/1000 sq. ft., based on a standard ASTM F-1869
(Calcium Chloride) test, or 80% rh, based on ASTM F-2170. A moisture content that is
too high will also slow the cure of the SLU and can affect the subsequent floor finish.
Most floor covering manufacturers will have acceptable limits for MVTR and their
recommendations must be followed. Consult with Custom’s technical representatives for
specific recommendations regarding CUSTOM’s SLU and your particular installation.
Definition, Formulation, and Performance Values of
Self-Leveling Underlayment
Self-leveling underlayment (SLU) for flooring consists of a blend of Portland and/or
calcium aluminate cements, inorganic aggregates, co-polymers, and chemical
modifiers, which form a flowable, self-leveling compound for leveling interior subfloors.
These components form a high compressive strength and flowable cementitious
compound, resulting in a flat-level surface that accepts all ceramic and natural stone tile
floor finishes. Many SLU manufacturers state that select self-leveling materials also
provide proper surface prep and acceptability under alternative floor finishes, such as
carpet, vinyl, linoleum, resilient, and hardwood flooring. Refer to the manufacturers’
published data sheets for compatibility with alternative floor finishes. Virtually all the
cementitious SLU sold today is mixed with water only; no liquid acrylic-latex additive is
required. The dry re-dispersible co-polymers in the manufacturer’s formulas provide
improved bond strength and flexibility. SLU is formulated with proprietary copolymers and
cements, which provide ultra high compressive values, in some materials in excess of
4000 psi. The high compressive value of SLU materials results in a floor assembly that
consistently passes all 14 cycles on an ASTM C627 Robinson Floor Test for most
applications. This ‘Extra Heavy Duty’ rating for the finished floor is crucial for floors that
are subject to heavy foot traffic and large equipment such as scissor lifts and pallet
jacks. Alternative self-leveling applications, such as those over hydronic tubing or electric
radiant heat systems, will provide a moderate service rating. Installations over wood joist
/ plywood subfloor installations can provide anywhere from a light commercial to a
standard residential service rating, depending on the specific assembly detail.
The versatility of cement based self-levelers allows for SLU pours that can be applied
from 1/8", all the way up to 1 1/2", or in some cases, up to 2" in total thickness. SLU
materials can also be feather-edged to transition to other floor finishes. Allowable
thicknesses will vary depending upon the manufacturer and the specific formula. Certain
proprietary formulas are available that provide an extended set for pumping. These are
designed for use in high ambient temperature conditions, or over large spans when
more time to float the material is required.
Cure rates of SLU materials provide for a fast setting underlayment that can accept
ceramic or natural stone tile set with modified thin set in as little as 4 hours and 12 to
14 hours for resilient flooring after the SLU is poured in place. This helps to minimize
project downtime and allows the work schedule to proceed more expeditiously.
Technical White Paper
SELF-LEVELING UNDERLAYMENTS
Details and Guidelines for Self-Leveling Underlayments
Details and installation guidelines for floor systems that include an SLU are outlined in
the Tile Council of North America Handbook for Ceramic, Glass, and Stone Tile
Installation. The handbook recommends crack-isolation membranes, such as
RedGard®, Custom 9240®, or CrackBuster Pro® from Custom Building Products over
concrete substrates including SLU in order to isolate existing and new cracks in the
substrate. Floor systems over SLU need to conform to IBC, IRC, and local building
codes. Maximum allowable substrate deflection (prior to the application of self-leveling
agent) is not to exceed l/360 under live load. For stone installations, maximum
allowable deflection in the substrate is l/720.
Common tile assembly including self-leveling underlayment:
TCNA F205-11 – Self-Leveling Underlayment over On Grade Concrete
Plywood subfloor engineered truss joist (TJI) systems can be encapsulated with a selfleveling agent. When installing an SLU over any wood framed plywood floor system,
application of metal or plastic lath mechanically anchored to the plywood sheathing is
essential to insure the integrity of the self-leveling installation, with the most common
reinforcement being a 2.5 lb. expanded metal lath. All plywood surfaces that are to
receive self-leveling should be coated with a latex primer that is formulated for use with
the self-leveling material. SLU over plywood sheathing truss joist floors must conform to
IBC, IRC, and local building codes. Maximum allowable substrate deflection (prior to
the application of self-leveling agent) should not exceed l/360 under live load. For stone
installations, maximum allowable deflection in the substrate is l/720. CUSTOM’s XP-1,
LevelQuik RS and LevelLite SLU can be applied to TJI or dimension lumber joist systems
can maintain up to 24" o.c. spans in the joist assembly.
Grout
CF205
Floors, Interior
Concrete Subfloor
Self-Leveling Underlayment, Bonded
Ceramic Tile
Latex Portland Cement Mortar
Self-Leveling Underlayment
Primer
Concrete Subfloor
Compatibility of Self-Leveling Applications as Part of a
Complete System Assembly.
Generally a cement-based self-leveling underlayment is a suitable surface for most
bonding mortars and adhesives. To assure compatibility, all installation products should
come from the same manufacturer. All Custom Building Products cement- or epoxybased thin-set mortar and grouting material are 100% compatible with CUSTOM SLU
products. So are CUSTOM’s waterproofing and crack isolation membranes, such as
RedGard®, Custom9240®, CrackBuster Pro®, or SpiderWeb Mat™. CUSTOM’s ability to
provide a complete system inclusive of SLU (LevelQuik or LevelLite), crack isolation and
waterproofing, uncoupling membrane (RedGard, Custom 9240, CrackBuster Pro or
SpiderWeb Mat), setting mortar (ProLite® or MegaLite®) and grout (Prism® SureColor®
or CEGLite® Commercial Epoxy Grout) makes single sourcing from one manufacturer a
simple process.
Execution and Cost Comparisons of Self-Leveling vs. Standard
Mortar Bed Installations
Perhaps the biggest benefit of a cementitious self-leveling floor prep assembly is the
inherent cost and labor savings it provides, particularly when compared to traditional
Technical White Paper
SELF-LEVELING UNDERLAYMENTS
cement mortar bed assemblies (ref. TCNA methods F111 & F112). In researching cost
comparison information for this paper, flooring contractors who specialize in both
traditional mortar bed and self-leveling applications indicate that self-leveling installations
cost an average of 25% to 35% less than a traditional mortar bed installation, including
materials and labor costs. A two-man crew can manually pour a self-leveling application
in a fraction of the time required to gauge, screed and tamp a traditional 4:1 mortar bed,
as described in TCNA details F111 and F112, and ANSI A108.1. Furthermore, compared
to mortar bed assembles, the efficiency of a self-leveling application insures that the
finished product will meet much higher tolerances in regards to floor flatness, with far
less labor and tooling of the material required. The cost savings noted above are
indicative of this enhanced efficiency.
In consulting with floor / surface prep sub contractors, many indicate that projects involving
floors in excess of 10,000 sq. ft., self-leveling is normally broadcast with automated
pumping equipment, operated by a two- or four-man crew. As the self-leveling material can
be applied to specific areas of the floor using a mechanical pumping method, far less
tooling of the SLU is required. Floor floats are used to broadcast the material over the floor
span and required to achieve the intended floor flatness. Some manufacturers provide
materials with extended set/cure times, allowing for a larger timeframe in which to heal
and smooth the material. This extended set is most beneficial when applying self-leveling
over large floor spans in one pour. Consult with the manufacturer prior to selecting a job
specific self-leveling product. Pumping of flowable self-leveling material can be executed
on high-rise projects, including buildings in excess of 20 floors.
For surfaces of less than 10,000 sq. ft., self-leveling is often manually mixed on site and
“bucket poured” onto the properly prepared floor finish.
Estimated per square foot weights of self-leveling installations are approximately 11 lbs.
for ceramic tile, and 13 lbs. for stone installations (9 and 11 lbs. per sq. ft. for
CUSTOM’s LevelLite), with a self-leveling underlayment at ½” in thickness, in standard
applications over plywood or concrete. Mortar bed installations are typically between 19
and 21 lbs. per square foot. With today’s lightweight building construction, this weight
differential can accommodate designer-preferred ceramic and stone tile flooring.
Self-Leveling Underlayment is ready for flooring in as few as 4 hours. This provides a
much faster cure rate compared to a mortar bed application, which requires a minimum
of 20 hours, and can be as much as 10 days, depending upon jobsite conditions (ref.
ANSI A108.02 – 4.2.2.1).
In many cases a concrete floor specification (section 03450) will not provide the flatness
required for the concrete substrate to be finished with a tile or stone installation. This
being the case, and given the efficiencies of the SLU method, the concrete contractor and
general contractor can pay less attention to subsurface tolerances when a self-leveling
underlayment is included in the tiling spec section, as the SLU method provides the most
efficient method for remedying concrete that is out of flatness tolerances for floor finishes.
If you want to be assured of a flat surface for installation of all floor coverings, a
self-leveling underlayment and cementitious patching materials provide:
•A cost effective floor finish compared to traditional floor prep methods such as
traditional mortar beds
•Finished floors that provide flatness and levelness characteristics far greater than
the requirements of TCNA and ACI 117
•Reduction in potential lippage conditions in the tile assembly
•The availability of self-leveling products formulated with post consumer recycled
content, which provide a floor with a lighter per square foot weight and contribute
to LEED® certification for the project
•A subsurface finish that provides for a faster, more efficient, and higher quality tile
installation
Technical White Paper
SELF-LEVELING UNDERLAYMENTS
Custom Building Products Answers the Challenges of the
Enhanced Floor Flatness Standards with LevelQuik®
AND CustomTech™
LevelQuik and CustomTech products are engineered to meet a wide
range of job requirements and address a variety of existing floor
conditions.
Formulated with Controlled Cure Technology (CCT™), LevelQuik RS Rapid Setting SelfLeveling Underlayment seeks its own level within minutes, and provides a high early
compressive strength that can accept thin-set bonded tile applications in 4 hours or less
after application. LevelQuik RS will maintain a compressive value of 4400 psi after a
complete 28-day cure, and can be applied up to 1" in thickness in a single pour.
LevelQuik can also be feather-edged for smooth transitions to adjacent floor conditions
and finishes.
With a 30-minute working time, LevelQuik® ES Extended Set Self-Leveling Underlayment
is ideal for large applications that require longer cure rates to allow for additional tooling
and working after pour. As a result, LevelQuik ES is ideal for large single or multi floor
projects that require the self-leveler to be pumped with mechanical pumping equipment.
LevelQuik ES is formulated for application in conditions that require as much as a 2"
thick leveling agent and that can be tooled down to a feather edge. This provides for
smooth transitions to other floor finishes and project conditions.
LevelQuik Latex Primer is recommended as a preparation for all surfaces prior to
treatment with any LevelQuik cementitious self-leveling material. LevelQuik Latex Primer
dries within 30 to 60 minutes, depending upon the project conditions (including
temperature and humidity), and it dramatically improves the adhesion of the SLU to the
substrate while controlling subsurface porosity.
Contributions of SLUs to LEED® and Green Building
One recent trend in the formulation of self-leveling underlayments is the addition of post
consumer recycled aggregates to enhance the materials’ contribution to LEED
certification and green building. CUSTOM has also identified the benefits of using postconsumer recycled aggregates to achieve a lighter weight formula. In some cases, the
selection of a so-called “lightweight” SLU can reduce the per square foot (psf) weight of
the floor by as much as two pounds per square foot. Exactly how much an SLU can
contribute to minimizing floor psf weights will depend on the thickness requirements of
the self-leveling agent as a floor leveler. The thickness of the SLU will vary based on the
existing conditions and thickness of the substrate, as well as transitions to other floor
finishes.
Custom Building Products Responds to LEED and Green Building
Requirements with LevelLite® Lightweight SLU.
Engineered with over 20% Post-Consumer recycled content, LevelLite from Custom
Building Products provides the highest level of Green contribution under LEED 4.1
compared to any other material in the cementitious self-leveling product category.
Formulated with a unique blend of high quality cements and aggregates, LevelLite
provides a subsurface that is up to 2 lbs. per square foot lighter than standard mortar
bed installations.
L evelLite can accept a thin-set / tile application in as few as 4 hours after pour, and can
be applied up to 2" in thickness in a single pour, down to a feather-edge for smooth
transitions to other floor surfaces. In addition, Calcium aluminate-based patching and
self-leveling materials provide high compressive value and performance, resulting in a
versatile surface preparation solution for a host of selected floor finishes.
Technical White Paper
SELF-LEVELING UNDERLAYMENTS
Custom Building Products Launches CustomTech™
To address the needs of all floor coverings, CUSTOM recently introduced
three new products designed for leveling the floor prior to the
installation of wood and vinyl flooring as well as ceramic and stone tile.
These products incorporate state-of-the-art aluminate cements to
achieve the performance the industry expects. They have been
designed for easy application and allow immediate installation of the
floor covering.
A High Compressive Strength SLU
CustomTech™ TechLevel™ XP-1
Premium Calcium Aluminum Based Self-Leveling Underlayment
For challenging floor leveling installations, Custom Building Products has developed
TechLevel XP-1, a premium high-performance calcium aluminate based self-leveling
underlayment. With a compressive value in excess of 5,000 psi, TechLevel XP-1 is
ideal for floors that are subject to heavy foot traffic and large equipment, such as scissor
lifts and pallet jacks. TechLevel XP-1 is an abrasion-resistant formula that requires less
surface preparation. TechLevel XP-1 can level floors from featheredge up to 2" in
thickness. It is the preferred choice for preparing concrete floors to receive alternative
finishes, such as resilient flooring. (Refer to ASTM section F710 for concrete floor prep
and flatness requirements for resilient floor finish.)
New Generation General Purpose Patching Compound
CustomTech GenPatch™ General Purpose Calcium Aluminate Based Patch
For general purpose trowel-applied patching of interior or exterior concrete substrates,
specify CUSTOM’s GenPatch Calcium Aluminate Cement Based Patching Compound.
GenPatch can accept floor finish and adhesive bond coat in 60-90 minutes, and can be
feather-edged, or applied up to 1" thick.
Provides an Easy-to-Apply High-Strength
CustomTech Silk™ Patching and Finishing Compound
As a calcium aluminate-based cementitious compound, CustomTech Silk provides the
best solution for challenging applications, such as ramping between floor finishes which
maintain a variation in plane, in a smooth, easy to apply, high-strength formula.
CustomTech Silk has a rapid cure compound that can accept a host of different floor
finishes, including tile, stone, and resilient flooring.
References:
Tile Council of North America (TCNA) –
Handbook for Ceramic Tile Installation 2011 48th Edition
American National Standards Institute (ANSI)
Specification for the Installation of Ceramic Tile – 2011
American Concrete Institute (ACI) 117
American Concrete Institute (ACI)
“Guide for Concrete Floor and Slab Construction”
TTL News Volume 10 – Issue 1 – February 2009
“The Floor Flatness Report” – Concrete International
– www.ACIelearning.org January 2011
ABW Construction – Woodinville, WA
Custom Building Products – www.custombuildingproducts.com
LEED is a Registered Trademark of U.S.G.B.C.
About the author
John Gallup is an Architectural Consultant for Custom Building Products, based in
the Seattle area, and is responsible for the Northwest Region. In his 20+ years in
the ceramic tile and flooring industry, John has been responsible for specification
consultation and development , project pre-construction meetings, and job installation
inspections. John is an 8 year member of the Puget Sound Chapter of the Construction
Specifications Institute.
Seal Beach, CA
Technical Services 800-282-8786
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